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172 Pre-attentive auditory processes in conscious and unconscious subjects studied by evoked potentials to complex tones
68
Abstracts
/International
Journal
for the assessment of dynamic changes in specific effort over time with high time resolution.
170 AUDITORY PROBE SENSITIVITY LOAD CHANGES IN A COMPLEX PARADIGM
TO WORKDUAL-TASK
P. Ullsperger Federal Institute for Occupational Safety and Health, Noeldnerstrasse 40-42, Berlin 10317, Germany The goal of this study was to explore the utility of the auditory probe technique of mental workload estimation in a complex dual-task paradigm (Humphrey and Kramer, 1994). In addition to a baseline auditory oddball task, fifteen subjects performed a mental arithmetic task and a gauge monitoring task in single and dual task conditions. The gauge-monitoring task consisted of six continuously updated gauges. The task was to reset each gauge as quickly as possible once its cursor had reached the critical zone. For the mental arithmetic task,fhe center of each gauge served as a display area for the operators and operands. Throughout task performance three types of auditory stimuli were presented: lOOOHz-tones as standards (80%1, 2OOOHz- tones as targets (10%) and, novel sounds (10%). In the oddball task subjects counted the number of target stimuli. In the workload tasks none of the auditory probes required a response. Event-Flated brain potentials (ERP) were recorded from the occurrence of the tones in both the baseline oddball task and in the three combinations of the gauge monitoring and arithmetic task. ERP eliciting events also included gauge-view samples and the onset of the mental arithmetic trials. ERPs were recorded from 30 channels with a Cz reference. Task performance was adversely affected by adding the dual task requirement. This change was reflected in the ratings obtained via the NASA-TLX workload scales. P30Cl amplitude of ERPs elicited by 2OOOHz-tones was sensitive only to the introduction of the workload tasks during which P300 was absent. The amplitude of the novelty P3 tended to follow the gradations of mental workload. The P3OOsfrom presentation of the arithmetic trials and from the gaugerviews both discriminate between single and dual task conditions. Significant correlations between ERP parameters and performance data stress the sensitivity of ERP measures as indices of individual resource allocation during mental work. On the other hand, it becomes obvious that numerous issues remain to be addressed prior to the inclusion of ERP measures in assessment of mental workload.
171 MODERATE ASYMMETRY BLE SIGN OF SYMPATHOTONE SUBJECTS WITH ELECTRICAL (EHS)
OF SSR AS A POSSIPREDOMINANCE IN HYPERSENSITIVITY
E. Lyskov’v 2, M. Sandstr6mz, K. Hansson Mild’, dev’
S. Medve-
of Psychophysiology
30 (1998)
7-94
Institute of Human Brain, National Institute for Working Life, P.O. Box 7654, S-907 13 Umei, Sweden Objectives. A little is known about possible physiological mechanisms of the specific form of environmental illness Electrical Hypersensitivity (EHS). The aim of the present study was to examine baseline characteristics of the central and autonomous regulation in EHS persons. Materials and methods. Twenty patients (11 female, 9 male, 47 + / - 5 years) participated in the study. Combination of skin (facial itching, tingling, redness) and neurasthenic symptoms (general fatigue, weakness, dizziness, headache) was typical. Patients associated these symptoms with exposure to VDU and other electrical appliances. An equal number of symptoms-free subjects (12 female and 8 male, 44 + / - 7 years) served as a control group. The investigation comprised of self-report measures, hormones assessment, testing of visual functions (acuity, contrast sensitivity, critical fusion frequency), blood pressure, heart rate and its variability, electrodermal activity, respiration, skin temperature, EEG and visual evoked potentials. Results. Several variables were found to be different in EHS and control groups. Patients had faster onset and higher amplitude of sympathetic skin responses to different sensor stimuli and to gasping. Moderate left-right hand asymmetry of SSR was found in EHS group in comparison with control (140 ms vs. 40 ms, and 326 PV vs. 173 WV respectively). Mean values of heart rate in rest conditions was higher in patients in comparison with control (inter beat intervals: 0.80 s vs. 0.90 s). Heart rate response to standing test was shorter in patients (0.26 s vs. 0.34 s), whereas deep breathing test caused similar responses. Patients had higher values of critical fusion frequency (43 Hz vs. 39 Hz) and increased amplitude of VEP fundamental harmonics. The data in general indicate tendency to sympathetic predominance and hyperresponsitivity to a wide range of external factors in persons with EHS.
SYMPOSIUM Care Unit
29: Psychophysiology in Intensive
172 PRE-ATTENTIVE AUDITORY PROCESSES IN CONSCIOUS AND UNCONSCIOUS SUBJECTS STUDIED BY EVOKED POTENTIALS TO COMPLEX TONES S.J. Jones The National Hospital, London, U.K. In normal subjects, synthesised instrumental tones were used to model environmental sounds more closely than the disconnected pure tones used for most AEP studies. Following a sudden change in pitch or timbre, symmetrically distributed Nl and P2 potentials maximal near the vertex were consistent with bilateral generators in the supratemporal plane. Superficially similar potentials occurring at the onset of the tone were more anteriorly distributed. The differential interfering effect of tones of the same or another timbre suggests that the
Abstracts
/International
Journal
potentials reflect processing of the whole sound “object’ rather than its individual spectral components. Still more anteriorly distributed potentials were evoked at the end of a period of rapid pitch modulation, or when one modulation pattern changed to another; these appear to represent the same process as is responsible for the “mismatch negativity“, depending on the functioning of an automatic sensory memory store and an internal clock whose resolution is in the order or milliseconds. These responses are being used to investigate the level of cortical functioning in various states of consciousness and unconsciousness. In comatose patients, whereas the responses to onset and simple spectral change are often preserved, those which depend on stream segregation, memory and internal chronometry are less often present and are generally absent in the vegetative state. The clinical usefulness of these responses has yet to be established, but there are interesting implications for understanding the nature of consciousness and awareness.
173 MMN MONITORING
IN COMATOSE
D. Morlet’ and C. Fischer’* ’ INSERM U 280 and ‘Clinical Neurophysiology lab, Hopital Boulevard Pinel, Lyon 69003, France
PATIENTS
Neurologique,
59
Mismatch negativity and Nl component have been continuously recorded in a group of 16 normals in order to assess their normal variability over time. They have also been monitored in unconscious and comatose patients in order to observe the pattern of recovery of MMN in relation with the recovery of awareness and consciousness. For that purpose a MMN monitoring system has been developed. In normals, MMN recording was performed during 3 hours. For 8 subjects, we could stimulate and record data from the beginning of the session onwards, without any interruption. Nl latency was found very stable. Nl amplitude continuously decreased during the first 50 minutes, and then remained constant. MMN pattern showed a large variability along time. However, except a slight decrease in the amplitude during the first 30 minutes, we found no systematic drift in MMN measurements along time. In patients, 3 studies have been designed. In a first one MMN and Nl have been monitored intraoperatively under barbiturates and benzodiazepines as anesthetic agent, and postoperatively until recovery of awareness. In the second study propofol has been used as anesthetic agent. EEG, earlymiddle-late auditory evoked potentials and MMN have been simultaneously monitored. In both experiments after anaesthesia was over, and even when the patients were quite aware and in a situation to answer questions, MMN was nevertheless absent. MMN has also been recorded in 50 patients in order to
of Psychophysiology
30 (1998)
7-94
69
correlate presence or absence of MMN with the functional status of the patient and with the level of consciousness.
174 USE OF CONDITIONED ERPS IN PATIENTS WITH PERSISTENT VEGETATIVE STATE
M. Signorino’*, S. D’Acunto’, M. Vallasciani’, L. Gironelli’, F. Angeleri’ ‘Clinica Neurologica - University of Ancona, Ospedale Di Torrette, Ancona, 60100 Italy *Istituto di Riabilitazione “S. Stefano”, Port0 Potenza Picena, Italy
The term “persistent vegetative state” (PVS) has been used since 1972 to describe a condition of patients with severe brain damage in whom coma has progressed to a state of wakefulness without detectable awareness (1). To prognosticate that the vegetative state is permanent is very important, especially for ethical reasons, but it requires time and observation. Despite arguments to the contrary (2) some authors (3) argue that ancillary tests (cerebral blood flow, cerebral metabolic, EEG and evoked potentials studies) are very helpful when appropriately applied. As far as event-related potentials are concerned, the literature report contradictory data on P300 (4,5). In our previous studies (6,7), the use an emotionally conditioned technique of the classic odd-ball paradigm resulted useful in facilitating P300 elicitation, with good prognostic value, in head injured comatmse patients. The present research was carried out to test the possibility of using such a conditioning technique in PVS patients with the aim of exploring the extent of their unconsiousness and trying to obtain prognostic information. Ten subjects with PVS lasting from at least 6 months were studied. In 5 subjects the PVS was caused by anoxic-ischemic encephalopathy, in 4 by head trauma, in 1 it was an encephalitis aftermath. The procedure consisted of 12 successive trials. In the initial 2 trials, only conventional tone bursts were administered (passive odd-ball phase). These were followed by 6 trials in which verbal stimuli with an emotional (the patient’s own name) or neutral content were coupled to the tones (conditioning phase). Finally, 4 further trials were given using the simple odd-ball to determine whether the responses ceased once the reinforcement was withdrawn (extinction phase). Only in 3 patients were P300 waves obtained: in 2 only in the passive odd-ball phase, in 1 only in the conditioning phase. In all 3 patients the PVS was caused by head trauma. These results led us to conclude that: a) PVS is an extremely severe condition from a cognitive point of view, not allowing even elementary processing; b) the PVS due to anoxic-ischemic encehalopathy, even if similar from a clinical point of view to that due to head trauma, is characterised by deeper disruption of the cognitive processing; c) the existence of mental activity in PVS remains a mystery and P300 isn’t a particularly reliable tool for revealing it.
Abstracts
/International
Journal
for the assessment of dynamic changes in specific effort over time with high time resolution.
170 AUDITORY PROBE SENSITIVITY LOAD CHANGES IN A COMPLEX PARADIGM
TO WORKDUAL-TASK
P. Ullsperger Federal Institute for Occupational Safety and Health, Noeldnerstrasse 40-42, Berlin 10317, Germany The goal of this study was to explore the utility of the auditory probe technique of mental workload estimation in a complex dual-task paradigm (Humphrey and Kramer, 1994). In addition to a baseline auditory oddball task, fifteen subjects performed a mental arithmetic task and a gauge monitoring task in single and dual task conditions. The gauge-monitoring task consisted of six continuously updated gauges. The task was to reset each gauge as quickly as possible once its cursor had reached the critical zone. For the mental arithmetic task,fhe center of each gauge served as a display area for the operators and operands. Throughout task performance three types of auditory stimuli were presented: lOOOHz-tones as standards (80%1, 2OOOHz- tones as targets (10%) and, novel sounds (10%). In the oddball task subjects counted the number of target stimuli. In the workload tasks none of the auditory probes required a response. Event-Flated brain potentials (ERP) were recorded from the occurrence of the tones in both the baseline oddball task and in the three combinations of the gauge monitoring and arithmetic task. ERP eliciting events also included gauge-view samples and the onset of the mental arithmetic trials. ERPs were recorded from 30 channels with a Cz reference. Task performance was adversely affected by adding the dual task requirement. This change was reflected in the ratings obtained via the NASA-TLX workload scales. P30Cl amplitude of ERPs elicited by 2OOOHz-tones was sensitive only to the introduction of the workload tasks during which P300 was absent. The amplitude of the novelty P3 tended to follow the gradations of mental workload. The P3OOsfrom presentation of the arithmetic trials and from the gaugerviews both discriminate between single and dual task conditions. Significant correlations between ERP parameters and performance data stress the sensitivity of ERP measures as indices of individual resource allocation during mental work. On the other hand, it becomes obvious that numerous issues remain to be addressed prior to the inclusion of ERP measures in assessment of mental workload.
171 MODERATE ASYMMETRY BLE SIGN OF SYMPATHOTONE SUBJECTS WITH ELECTRICAL (EHS)
OF SSR AS A POSSIPREDOMINANCE IN HYPERSENSITIVITY
E. Lyskov’v 2, M. Sandstr6mz, K. Hansson Mild’, dev’
S. Medve-
of Psychophysiology
30 (1998)
7-94
Institute of Human Brain, National Institute for Working Life, P.O. Box 7654, S-907 13 Umei, Sweden Objectives. A little is known about possible physiological mechanisms of the specific form of environmental illness Electrical Hypersensitivity (EHS). The aim of the present study was to examine baseline characteristics of the central and autonomous regulation in EHS persons. Materials and methods. Twenty patients (11 female, 9 male, 47 + / - 5 years) participated in the study. Combination of skin (facial itching, tingling, redness) and neurasthenic symptoms (general fatigue, weakness, dizziness, headache) was typical. Patients associated these symptoms with exposure to VDU and other electrical appliances. An equal number of symptoms-free subjects (12 female and 8 male, 44 + / - 7 years) served as a control group. The investigation comprised of self-report measures, hormones assessment, testing of visual functions (acuity, contrast sensitivity, critical fusion frequency), blood pressure, heart rate and its variability, electrodermal activity, respiration, skin temperature, EEG and visual evoked potentials. Results. Several variables were found to be different in EHS and control groups. Patients had faster onset and higher amplitude of sympathetic skin responses to different sensor stimuli and to gasping. Moderate left-right hand asymmetry of SSR was found in EHS group in comparison with control (140 ms vs. 40 ms, and 326 PV vs. 173 WV respectively). Mean values of heart rate in rest conditions was higher in patients in comparison with control (inter beat intervals: 0.80 s vs. 0.90 s). Heart rate response to standing test was shorter in patients (0.26 s vs. 0.34 s), whereas deep breathing test caused similar responses. Patients had higher values of critical fusion frequency (43 Hz vs. 39 Hz) and increased amplitude of VEP fundamental harmonics. The data in general indicate tendency to sympathetic predominance and hyperresponsitivity to a wide range of external factors in persons with EHS.
SYMPOSIUM Care Unit
29: Psychophysiology in Intensive
172 PRE-ATTENTIVE AUDITORY PROCESSES IN CONSCIOUS AND UNCONSCIOUS SUBJECTS STUDIED BY EVOKED POTENTIALS TO COMPLEX TONES S.J. Jones The National Hospital, London, U.K. In normal subjects, synthesised instrumental tones were used to model environmental sounds more closely than the disconnected pure tones used for most AEP studies. Following a sudden change in pitch or timbre, symmetrically distributed Nl and P2 potentials maximal near the vertex were consistent with bilateral generators in the supratemporal plane. Superficially similar potentials occurring at the onset of the tone were more anteriorly distributed. The differential interfering effect of tones of the same or another timbre suggests that the
Abstracts
/International
Journal
potentials reflect processing of the whole sound “object’ rather than its individual spectral components. Still more anteriorly distributed potentials were evoked at the end of a period of rapid pitch modulation, or when one modulation pattern changed to another; these appear to represent the same process as is responsible for the “mismatch negativity“, depending on the functioning of an automatic sensory memory store and an internal clock whose resolution is in the order or milliseconds. These responses are being used to investigate the level of cortical functioning in various states of consciousness and unconsciousness. In comatose patients, whereas the responses to onset and simple spectral change are often preserved, those which depend on stream segregation, memory and internal chronometry are less often present and are generally absent in the vegetative state. The clinical usefulness of these responses has yet to be established, but there are interesting implications for understanding the nature of consciousness and awareness.
173 MMN MONITORING
IN COMATOSE
D. Morlet’ and C. Fischer’* ’ INSERM U 280 and ‘Clinical Neurophysiology lab, Hopital Boulevard Pinel, Lyon 69003, France
PATIENTS
Neurologique,
59
Mismatch negativity and Nl component have been continuously recorded in a group of 16 normals in order to assess their normal variability over time. They have also been monitored in unconscious and comatose patients in order to observe the pattern of recovery of MMN in relation with the recovery of awareness and consciousness. For that purpose a MMN monitoring system has been developed. In normals, MMN recording was performed during 3 hours. For 8 subjects, we could stimulate and record data from the beginning of the session onwards, without any interruption. Nl latency was found very stable. Nl amplitude continuously decreased during the first 50 minutes, and then remained constant. MMN pattern showed a large variability along time. However, except a slight decrease in the amplitude during the first 30 minutes, we found no systematic drift in MMN measurements along time. In patients, 3 studies have been designed. In a first one MMN and Nl have been monitored intraoperatively under barbiturates and benzodiazepines as anesthetic agent, and postoperatively until recovery of awareness. In the second study propofol has been used as anesthetic agent. EEG, earlymiddle-late auditory evoked potentials and MMN have been simultaneously monitored. In both experiments after anaesthesia was over, and even when the patients were quite aware and in a situation to answer questions, MMN was nevertheless absent. MMN has also been recorded in 50 patients in order to
of Psychophysiology
30 (1998)
7-94
69
correlate presence or absence of MMN with the functional status of the patient and with the level of consciousness.
174 USE OF CONDITIONED ERPS IN PATIENTS WITH PERSISTENT VEGETATIVE STATE
M. Signorino’*, S. D’Acunto’, M. Vallasciani’, L. Gironelli’, F. Angeleri’ ‘Clinica Neurologica - University of Ancona, Ospedale Di Torrette, Ancona, 60100 Italy *Istituto di Riabilitazione “S. Stefano”, Port0 Potenza Picena, Italy
The term “persistent vegetative state” (PVS) has been used since 1972 to describe a condition of patients with severe brain damage in whom coma has progressed to a state of wakefulness without detectable awareness (1). To prognosticate that the vegetative state is permanent is very important, especially for ethical reasons, but it requires time and observation. Despite arguments to the contrary (2) some authors (3) argue that ancillary tests (cerebral blood flow, cerebral metabolic, EEG and evoked potentials studies) are very helpful when appropriately applied. As far as event-related potentials are concerned, the literature report contradictory data on P300 (4,5). In our previous studies (6,7), the use an emotionally conditioned technique of the classic odd-ball paradigm resulted useful in facilitating P300 elicitation, with good prognostic value, in head injured comatmse patients. The present research was carried out to test the possibility of using such a conditioning technique in PVS patients with the aim of exploring the extent of their unconsiousness and trying to obtain prognostic information. Ten subjects with PVS lasting from at least 6 months were studied. In 5 subjects the PVS was caused by anoxic-ischemic encephalopathy, in 4 by head trauma, in 1 it was an encephalitis aftermath. The procedure consisted of 12 successive trials. In the initial 2 trials, only conventional tone bursts were administered (passive odd-ball phase). These were followed by 6 trials in which verbal stimuli with an emotional (the patient’s own name) or neutral content were coupled to the tones (conditioning phase). Finally, 4 further trials were given using the simple odd-ball to determine whether the responses ceased once the reinforcement was withdrawn (extinction phase). Only in 3 patients were P300 waves obtained: in 2 only in the passive odd-ball phase, in 1 only in the conditioning phase. In all 3 patients the PVS was caused by head trauma. These results led us to conclude that: a) PVS is an extremely severe condition from a cognitive point of view, not allowing even elementary processing; b) the PVS due to anoxic-ischemic encehalopathy, even if similar from a clinical point of view to that due to head trauma, is characterised by deeper disruption of the cognitive processing; c) the existence of mental activity in PVS remains a mystery and P300 isn’t a particularly reliable tool for revealing it.